Refrigerated vapor degreasing method

Abstract

A method of vapor degreasing workpieces using a refrigerated vapor degreasing system. The system has a tank for containing a bath of degreasing solvent, a heater for vaporizing the solvent, a primary solvent condenser, a secondary solvent condenser, and a single refrigeration unit which can be switched to operate in two different modes. Workpieces are loaded and supported within the tank. The degreasing solvent is heated and evaporated in the tank. Refrigerant is cycled in a closed-loop, single compressor refrigeration system as low-pressure/low-temperature vapor, high-pressure/high-temperature vapor, high-pressure/low-temperature liquid, low-pressure/low-temperature vapor, and low-pressure/low-temperature liquid. A degreasing zone is formed around the workpiece and a primary evaporation barrier is formed above the workpiece by circulating low-pressure/low-temperature refrigerant from the refrigeration system through the primary solvent condenser located above the workpiece. The evaporated degreasing solvent condenses on the workpiece in the degreasing zone to clean the workpiece. A secondary evaporation barrier is formed above the degreasing zone by circulating low-pressure/low-temperature refrigerant from the refrigeration system through the secondary solvent condenser located above the degreasing zone. The secondary solvent condenser is intermittently defrosted by circulating high-pressure/high-temperature refrigerant from the refrigeration system through the secondary solvent condenser.

I claim: 
     
       1. Method of vapor degreasing workpieces, comprising the steps of: a) supporting the workpieces in a tank;   b) evaporating a degreasing solvent in the tank;   c) cycling refrigerant in a close-loop, single compressor refrigeration system as low-pressure/low temperature vapor, high-pressure/high temperature vapor, high-pressure/low-temperature liquid, low-pressure/low-temperature vapor, and low-pressure/low-temperature liquid;   d) forming a degreasing zone around the workpieces and a primary evaporation barrier above the workpieces by circulating low-pressure/low-temperature refrigerant from said refrigeration system through a primary solvent condenser located above the workpieces, said evaporated degreasing solvent condensing on the workpieces in the degreasing zone to clean the workpiece;   e) forming a secondary evaporation barrier above the degreasing zone by circulating low-pressure/low-temperature refrigerant from said refrigeration system through a secondary solvent condenser located above the degreasing zone; and   f) intermittently defrosting the secondary solvent condenser by circulating high-pressure/high temperature refrigerant from said refrigeration system through the secondary solvent condenser.   
     
     
       2. The method recited in claim 1 said decreasing zone being formed by condensing vaporized solvent on the workpieces, and said primary solvent condenser which have a temperature less than the vaporized solvent. 
     
     
       3. The method recited in claim 1, said secondary evaporation barrier being formed by circulating refrigerant through said secondary solvent condenser at a temperature less than the temperature of the refrigerant circulating through said primary solvent condenser. 
     
     
       4. The method recited in claim 1, said secondary solvent condenser being defrosted by temporarily restricting the flow of low-pressure/low-temperature refrigerant through said condenser, and circulating high-pressure/high temperature refrigerant through said condenser. 
     
     
       5. The method recited in claim 1, including the step of selectively opening and closing a series of metering valves in the refrigeration system so that: a) in a first mode, low-pressure/low-temperature refrigerant flows through said primary solvent condenser and said secondary solvent condenser; and   b) in a second mode, low-pressure/low temperature liquid refrigerant flows through said primary solvent condenser and high-pressure/high-temperature vapor refrigerant flows through said secondary solvent condenser.   
     
     
       6. The method recited in claim 5, including the step of calibrating said metering valves and opening or closing respective serially-aligned solenoid valves. 
     
     
       7. Method of cleaning workpieces in a vapor degreasing tank, comprising the steps of: a) evaporating a chemical degreasing solvent   b) cycling refrigerant in a closed loop, single compressor refrigeration system as low-pressure/low-temperature vapor, high-pressure/high-temperature vapor, high-pressure/low-temperature liquid, and low-pressure/low-temperature liquid.   c) forming a degreasing zone by condensing the vaporized solvent proximate the workpiece by circulating the low-pressure/low-temperature refrigerant through primary condensing coils located intermediate the degreasing tank, said evaporated solvent condensing on the workpieces in the degreasing zone to clean the workpieces;   d) forming a cold air trap above the degreasing zone by also circulating the low-pressure/low-temperature refrigerant through cold trap condensing coils located proximate the top of the degreasing tank; and   e) intermittently defrosting the cold trap condensing coils by temporarily restricting the flow of the low-pressure/low-temperature refrigerant through the cold trap condensing coils and circulating high-pressure/high-temperature refrigerant through the cold trap condensing coils.